In the Oos district of Baden-Baden, a new wastewater sewer was constructed along the perimeter of the Oos-West industrial estate, to replace an obsolescent DN 450 pressure main. The sewer had to be constructed along a new route, since the path of the old pressure main ran directly under the estate, and its direct replacement would have made the further development of the area difficult. In planning the new construction, Baden-Baden’s municipal environmental-engineering operator, the “Umwelttechnik” department, decided against installing a new pressure main and instead opted for a gravity sewer; due to the special requirements, it was decided to install systems consisting of vitrified-clay pipes.

The project was planned by Wald+Corbe Infrastrukturplanung GmbH. Since the construction project lies in the middle of a region of great importance for the drinking-water supply, and is also within the protection zone for the hot springs for which Baden-Baden is renowned, an open-trench installation of the water-drainage system was out of the question. It was therefore decided to install the pipes that would be below the groundwater table using the pipe jacking method, with just a small section of the system above the groundwater table being constructed by the open-trench method. Vitrified-clay pipes of the DN 800 standard size were used throughout both sections of the sewer system.

The starting date for the construction project was set for September 2013.

The project involved the following construction operations

Excavation of the sink shafts

4 shafts with a diameter of 2,600 mm

5 shafts with a diameter of 3,200 mm

Installation of the pipes

1,200 m pipe jacking, DN 800 pipes

270 m open-trench installation, DN 800 pipes

Installation of a pump shaft

Diameter of 3,200 m at a depth of 11.65 m

The pipe-jacking work was conducted around the clock using an MTS 1000 system displacing the soil with flushing. The maximum necessary jacking force that was achieved was 130 t, and the average jacking distance was 38 m per day. Pipe jacking started with four separate pipeline sections over a distance of approx. 600 m in soft clays, using a high-pressure flushing system. Pipeline sections five to eight (also over a distance of approx. 600 m) were jacked through subsoils consisting of material ranging from fine sand to coarse gravel (stones with an edge length up to 0.30 m). The amounts of gravel and stones that had to be extracted from the ground made great demands on the machines and equipment, but generally the pipe jacking process could be completed without any major problems. Only the cutting wheel had to be reconditioned at the end of each section, since the stones in the ground had taken their toll on them. The individual jacking sections were between 150 m and 160 m in length.

The new wastewater pipeline has now been in operation since April 2014.